Hive used to be Steem but it forked from that blockchain back in 2020. I wrote a post about that a few weeks ago on my alternate @holovision.cash account:
@holovision.cash/the-rise-of-hive-going-on-three-years-of-being-better-than-steemit
For the nuances you have to go back to a bunch of posts made back in 2020 and old internet articles buried in the search engine. Articles such as this one: https://decrypt.co/29416/steem-network-to-seize-5-million-from-its-own-users
Short version story: I think you probably understand staking. HIVE and STEEM are both delegated Proof of stake. You can't mine the token directly. New HIVE and STEEM are minted by "witnesses" of the blockchain.
The team of people that originally built Steemit had a huge amount of pre-mined STEEM tokens locked. Because this gave them a huge amount of influence over the blockchain certain assurances were made to the community.
Then a billionaire named Lex Luthor...Sorry, I meant Justin Sun came along and bought Steemit, INC with the plan to use a nuclear missile to create a massive earthquake that...Sorry, got him confused again with Lex Luthor.
Anyway, TRON blockchain "owner" Justin Sun bought Steemit, Inc. which came along with all of the pre-mined STEEM tokens that were locked away with assurances that Justin Sun wasn't interested in honoring anymore now that he "owned" the STEEM blockchain. With all that STEEM Justin Sun could, and I would argue has, made the STEEM blockchain more centralized.